Telegraph signal distortion measuring apparatus and system



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W, R ETAL 2,3@?,23? TELEGRAPH SIGNAL DISTORTION MEASURING APPARATUS ANDSYSTEM Filed March 29, 1941 2 Sheets-Sheet l W 2" REfl JRW/LM'RSONATTORNEY Jan. 5, 1943. w. T. REA HAL 2,307,237

TELEGRAPH SIGNAL DISTORTI ON MEASURING APPARATUS AND SYSTEM Filed March29, 1941 2 Sheets-Sheet 2 /66 /.67\ v f 7 SPAC/NG\\ v MARKWG /N N RS W$R A y JRWILKERSON QMM' ATTQRMEV alenled .lan.

one arrnaa'rps SYSTEM Wilton T. Rea, Wayside, and .lleflerson R.Wilkerson, New York, N. l(., assignors to Bell Telephone Laboratories,Incorporated, N ew York, N. in, a corporation oi New York ApplicationMarch 29, 1941, Serial No. 385,802

22 Claims.

This invention relates to telegraph testing equipment and, moreparticularly, to telegraph testing apparatus employing a cathode raytube for indicating both the type and the amount of bias and distortionpresent in telegraph signals.

It is an object of this invention to provide a telegraph system with anindicating device which may be easily connected directly into atelegraph system while it is in service for indicating, Withoutdisturbing the transmission of signals, both the type and the amount ofbias and distortion present in telegraph signals transmitted over thesystem.

It is also an object of the invention to provide a telegraph distortionindicator with a cathode ray tube for readily indicating both the typeand the amount of bias and distortion possessed by each impulse of atelegraph permutation code signal combination, each impulse beingassigned a different indicating area on the screen of the cathode raytube.

Another object of the invention is to provide the telegraph distortionindicator with means for preventing the production of parasitic spots onthe screen of the cathode ray tube that might otherwise be caused by thechattering of the armature of the receiving relay.

These and other objects of the invention are accomplished by providingthe cathode ray tube of the distortion indicator-with a dampedsinusoidal oscillatory sweep circuit having two voltages 90 degrees inquadrature and designed to cause the cathode ray beam to follow alogarithmic spiral path at the rate of one revolution per pulse of theincoming signal and to make six and one-half revolutions for each fiveunit telegraph permutation code signal combination and an additionalrevolution for each additional unit of the code. side the top edge ofthe tubes screen and move in a logarithmic spiral path curving in towardthe center of the screen. Due to the decrement of the oscillatorycircuit, the electron beam enters the indicating area of the screenapproximately half way through the start pulse. The decrement, ordamping, of the oscillatory circuit is controlled by a vacuum tubeand'the circuits are tuned to cause the beam to make a completerevolution in the time allotted to each impulse of the permutation codesignal combination. This also controls the spacing between the adjacentturns of the spiral. Since the path of these revolutions ultimatelyapproaches the center of the screen of the tube, means are provided forThese revolutions start outquickly returning the beam to its initialstarting position at the outer edge of the tube for making anotherseries of convolutions.

The potential applied to the intensity control electrode of the tube ismade sufficiently negative so that ordinarily the beam is invisible. Inresponse to each transition of the line current, a short positiveimpulse is applied to the intensity control electrode of the tube toproduce a momentarily visible spot of light on the screen. In the caseof an undistorted signal, there would be a row of visible spots, orflashes, along a radius of the screen. Distortion of the signals willcause displacement of the flashes from this line, the angulardisplacement being proportional to the amount of the bias anddistortion. Consequently, the amount of bias and distortion may be readin terms of the percent oi the displacement on a radial scale in whichper cent is equal to 360 degrees of arc. The type of bias and distortionis indicated by the position of the flash in respect to the normalradial line; that is, whether the flash is in advance of the radial lineor behind it.' A half wave copper-oxide rectifier, or varistor, isincluded in the intensity control circuit to prevent the production ofparasitic spots on the screen that might otherwise be caused by thechattering of the contacts of the receiving relay.

These and other features of the invention will be described in detail inconnection with the description of the drawings, in which:

Fig. 1 is a circuit diagram 01' the distortion indicator;

Fig. 2 is a graphical representation of the voltages applied to theelectron beam deflecting electrode of the cathode ray tube;

Fig. 3 is a graphical representation of a startstop permutation codesignal combination; and,

Fig. 4 is a diagrammatic view showing the path of impingement of theelectron beam upon the screen of the cathode ray tube.

Referring now to Fig. 1, the reference numeral ll designates a signalresponsive polarized relay. Across the operating winding of relay llinput jack I2 is connected so that telegraph signals may be appliedacross the operating winding 01' the relay in the direction to opposeand overcome the effect of the biasing winding of the relay. The"biasing winding is connected through resistor I! to battery conductor I,over which current is supplied from grounded battery I6. The armature ofrelay II is connected to ground and is operable between the contacts I!and It.

For convenience in describing the system, the

armature is shown engaging the contact I1, and all other circuitconditions correspond-thereto. This is the condition of relay whenresponding to a marking impulse and although a source of telegraphsignals has not been shown applied to jack |2, it is to be assumed thatrelay H is responding to a marking impulse. Relay contact I1 isconnected to one end of the operating winding of a polarized relay l3,the other end of which is connected through resistor 2| and batteryconductor l3 to grounded battery l3. The operating winding of polarizedrelay l3 thus is energized to oppose and overcome the biasing winding,one end of which is connected through resistor 23 to battery conductor 3and the other end of which is connected through resistor 22 to ground.

The armature of polarized relay I3 is connected to battery conductor l3and thus to battery l6 and is operable between contacts 23 and 23. Thecontact 23 which the armature of relay l3 engages when the operatingwinding of the relay is energized is connected through resistor 23 toone side of an oscillatory circuit which consists essentially of theinductance 21 and condenser 23 in parallel. The branch of theoscillatory circuit which contains the inductance 21 includes in serieswith the inductance the secondary winding of a feedback transformer 23and resistors 3| and 32. potential d vider resistors 33 and 33 in seriesacross the condenser 23. The terminal of condenser 23 which is connectedto the resistors 32 and 33 is connected to ground, whereby two paths forcurrent through the armature of relay l3 and resistor 23 are provided.one extending through inductance 21, the secondary of transformer 23,resistors 3| and 32 to ground, and the other extending through resistors33 and 33 to ground. Current through this network causes condenser 23 tobecome charged to the potential difierence across the resistors 33 and33 in series. The point of interconnection of the secondary oftransformer 23 and the resistor 3| is connected to grid 33 and the pointof interconnection of resistors 33 and 33 is connected to grid 31 of atwin triode amplifier-tube 33 which is provided with the usualindirectly heated catho e 39.

The resistors 33 and 33 are of such value that when the receipt of astart signal permits the circuit to oscillate, the total resistanceacross said resistors causes the condenser voltage to be in quadraturewith the voltage developed across resistors 3| and 32. That part of thevoltage across condenser 23 which is represented by the potentialdiflerence across resistor 33 is applied to grid 31 of tube 38 and thepotential difference across resistors 3| and 32 is applied to grid 33 ofthe tube. Thus the voltages of grids 36 and 31 are in quadrature.

Plate 3| of tube 33 which is controlled by grid 33 is connected to thevertical deflecting plate 32 of a cathode ray tube 33 and plate 33 ofthe tube 33, which is controlled by grid 31 is connected to thehorizontal deflecting plate 33 of cathode ray tube 33. Plate potentialfor the plates 3| and 33 of tube 38 is obtained from high voltageconductor 31 of full wav rectifier tube 33 through potentiometers 39 and5|, respectively, at the high potential end of a voltage divider whichconsists of the paralleled potentiometers 33 and 3| in series withresistors 52, 33, 33 and 33, the latter of which represents the lowpotential end of the potential divider and has its free end connected toground. High potential conductor 31 The oscillatory circuit alsoincludes 01 the rectifier includes a filter consisting of the inductance31 and condensers 33 and 33. Positive potential is applied frompotentlometers 33 and 3| to plates 3| and 33, respectively, through theload resistors 3| and 32, respectively.

The contact 23 of polarized relay I9 is connected through resistors 33and 33 to ground. One end of the biasing winding of a polarized relay 31is connected through resistor 63 to ground and the other end isconnected through resistor 66 to battery conductor I3. The operatingwinding of polarized relay 31 has one end connected to battery conductorI3 through reslstor 38 and the other end of the winding is connected toback contact 69 of relay 61 and to one side of condenser 1| the otherside of which is connected through resistor 12 to ground. The armatureof relay 61, which is operable between contact 69 and a front contact 13is connected to ground. From this it will be apparent that the operatingwinding of relay 31 may become energized through its armature andcontact 13 or through a charging current for condenser 1|.

The contact 13 of relay 31 is connected directly to the ground side ofthe biasing winding of relay l9. When the armature of relay 61 engagescontact 13, the ground connection for the biasing winding of relay I9supplied through resistor 22 is short-circuited and the biasing windingof relay IQ is connected directly to ground, whereby the current throughthat winding is increased. The increase is sufficient to give thebiasing winding sole control over relay l3 so that its armature will bemaintained in engagement with the contact 23 and will not be movedduring subsequent energization of the operating winding of relay l9.

As previously stated, the voltages applied to grids 33 and 31 ofamplifier tube 33 by the oscillatory circuit, the principal componentsof which are the condenser 23 and inductance 21, are in quadrature. Theresistors associated with the oscillatory circuit are so proportionedthat the voltages in quadrature phase are equal in amplitude. Thesevoltages are amplified by the tube 33 and are applied to one each of thehorizontal and vertical deflecting plates 36 and 32, respectively, ofcathode ray tube 33. Other capacitances such as the condensers 13, 15and 16, may be connected in parallel with the condenser 23 selectivelyby means of the keys 11, 18 and 19, respectively, to change thefrequency of oscillation of the oscillatory circuit.

The resistor 3| previously identified as being in the circuit of grid 33of amplifier tube 29, is in the form of a potentiometer and its slider3| is connected to the grid 33 of a feedback amplifier tube 86 which maybe a triode tube having an indirectly heated cathode 31. The plate 33 oftube 36 is connected to one end of the primary winding of transformer29, the other end of which is connected by conductor 92 to the platevoltage conductor 31. A condenser 93 is connected across the primarywinding of feedback transformer 23, and the function of the condenser 93is to adjust the phase of the current in the feedback circuit whichincludes the plate of tube 33, so that it will be in phase with thecurrent in the oscillatory circuit comprising the inductance 21 and thecondensers 28, 13, 15

and 16 or whatever number of those condensers are connected in aparallel, so that the current fed back into the oscillatory circuit willbe in phase with the current locally generated in the oscillatorycircuit. The secondary of feedback transformer 21 being in series withinductance 21 in the oscillatory circuit, the currents traversing theprimary winding of feedback transformer 29 are impressed upon theoscillatory circuit which feeds the grids 98 and 91 of amplifier tube99.

In addition to the electrodes 92 and 99 the cathode ray tube 93 has twoother electrodes 99 and 98 for controlling the deflection oi' theelectron beam and the electrodes 99 and 99 are connected to the lowpotential side of a half wave rectifier which includes tube 97. Thecathode ray tube also has an electrode I99 by which the intensity of"the electron beam is controlled. This electrode is connected throughconductor I98 and blocking condenser Illi to one side of condenser Iiiand to one end of resistor I99, the other end of which is connected toground. The other side of condenser III is connected to one end of thewinding of a retardation coil H2. The other end of the winding ofretardation coil H2 is connected to one terminal of a half wavecopperoxide rectifier H9 and the other terminal oi'the rectifier isconnected to the right-hand stationary springs H9 and H9 or single anddouble keys iii and H9, respectively. The halfw ave rectifier II 9 issometimes called a varistor due to the fact that it readily passesdirect current in one direction and greatly retards passage of directcurrent in the other direction. Thus it may be considered as having thecharacteristics of a variable resistor offering low resistance to thepassage of current in one direction and extremely high resistance to thepassage of current in the other direction.

The key III is a single-pole double-throw key. the swinger I I9 of whichis biased to engage the left-hand stationary spring I2I. Swinger M9 isconnected to the contact I9 of polarized relay II through resistor I22and the left-hand stationary spring MI is connected through resistor I29to battery conductor I9. Stationary spring I is also connected to theleft-hand swinger spring I26 of key M9 which is a double-throw key. Thestationary spring I29 with which swinger I129 cooperates and intoengagement with which the swinger I29 is normally biased, is connectedto swinger H9 01' key Ill and thus through resistor I22 to contact iiiof polarized relay II. The right-hand swinger spring I29 of key H8 isconnected to the point of interconnection of the operating winding ofrelay i9 and the resistor 2 I.

A power supply for the cathode ray tube 99 comprises a transformer ml,the primary winding of which is connected to a source of alternatingcurrent 992, the rectifier tube 91 connected across the high voltagesecondary winding of transformer I9I as a half wave rectifier,potentiometers 993 and I39 connected between the plates of rectifiertube 99 and the high voltagewinding of transformer II9I for supplyingthe proper biasing voltages to the intensity control electrode I199 andfocussing electrode of the cathode ray tube, and filter condensers I36for filtering out the alternating components of the output of rectifiertube 91. The transformer I9I also supplies current for operating therectifier 99 and the cathode heaters of amplifier tubes 99 and 89 ofcathode ray tube 99.

The control exercised over the cathode ray tube 99 by the systemhereinbefore described affects the intensity of the beam of electronsand the deflection of that beam. The intensity of the beam is controlledby the control grid I". The

deflection of the beam is controlled jointly by the pair of horizontaldeflecting plates 46 and 98 and the pair of vertical deflecting plates42 and 99. For the purposes of the description of the operation of thesystem, it will first be assumed that a rest impulse which is a steadymarking condition is applied through the Jack I2 to the operatingwinding of polarized relay II.- It will also be assumed that neither ofthe keys Ill and H8 is operated and therefore that they remain in thecondition shown in Fig. 1.

With operating winding of polarized relay II energized, the effect ofthe biasing winding is overcome and the armature of the relay is held inengagement with the back contact I'I. Thus ground is connected throughcontact I1 and through the operating winding of polarized relay I9,through resistor 2| to grounded battery I9, whereby the operatingwinding of polarized relay I9 overcomes the effect of the biasingwinding and the armature is held in engagement with back contact 22.Since battery It is connected to the armature of polarized relay I9,positive battery is connected to the armature and through contact 23 andresistor 26 to the oscillatory circuit consisting essentially of theinductance 21 and as many of the condensers 28, I9, I5 and I9 as areconnected into the circuit by having their keys I1, 18 and 79 closed.The flow of current is from grounded battery It through the armature ofpolarized relay I9, contact 22, resistors 29, 99 and 39 to ground, andthrough inductance 27, secondary of transformer 29, and resistors 9i and32 to ground. Theflow of current main tains a charge on the condensersat least one of which, having the reference numeral 28, is permanentlyconnected in the oscillatory circuit. The potential difierence acrossthe resistor 39 due to the flow of current therethrough provides abiasing voltage for the grid 31 of amplifier tube 99, and the flow ofplate current through load resistor 62 of plate 99 provides a steadypotential of low value across the horizontal deflecting plates 99 and 96of cathode ray tube 93 with plate 96 slightly negative with respect toplate 99. Since current also flows through inductance 21, secondary oftransformer 29, and resistors 3i and 92 to ground, the potentialdifference across resistors 3| and 32 establishes a biasing potentialfor the grid 36 of amplifier tube 98 at a certain level above ground andthis bias is preferably of a relatively high value so' that considerableplate current flows through the load resistor iii of 'plate 9i andaii'ords a high negative potential upon the vertical deflector plate 92of cathode ray tube 99 with reference to the potential of deflectorplate 99 which is connected to the junction of resistors 52 and 53. Inactual practice. the potential difference between horizontal deflectingplates 96 and 99 is very low so as to defleet the electron beam in thecathode ray tube 99 horizontally only to an insignificant extent and thepotential difference between vertical deflecting plates 92 and 99 issuificiently high to deflect the beam beyond the limits of the screen ofthe cathode ray tube. Thus the beam is defiected almost vertically andits point of impingement is outside the limits of the screen.

The polarized relay 91 has its operating winding energized by currentfrom grounded battery It through resistor 68, operating winding of relay91, back contact 69 of the relay and armature to ground. The biasingwinding of polarized relay 91 is also energized from battery I6 throughresistor 86, biasing winding of the relay and resistor (it to ground,and the biasing winding overcomes operating winding and holds thearmature on contact 69.

Upon the transmission of a start-stop permutation code signalcombination through jack l2, the start impulse, which is of spacingnature, cuts off the current through the operating winding of relay I i,in the case of current-no-current signals, or reverses the currentthrough that winding, in the case of polar signals. When polar signalsare received, the biasing winding is left open and is not used. Ineither case the armature of polarized relay Ii moves out of engagementwith contact I! and into engagement with contact i8. Thus the circuit ofthe operating winding of polarized relay I9 is interrupted and thearmature of that relay moves out of engagement with contact 23 and intoengagement with contact 2 3. Battery is thus removed from theoscillatory circuit and is connected through contact 26 and throughresistor 63 and resistor M to ground. The resistor 63 is thus placed inparallel with the resistor 66 and the biasing winding of relay 67between grounded battery l6 and resistor 66. The resistance value ofresistor 63 is relativel low as compared with the combined resistance ofresistor 66 and biasing winding of relay iii in series, so that a partof the current through resistor 66 is diverted through resistor 63 andthe current through the biasing winding of relay 61 is materiallyreduced. The operating winding of relay 6'! thus assumes control of thearmature and moves the armature into engagement with the front contact13. As the armature moves out of engagement with contact 69, ground isdisconnected from the operating winding of relay 6? but that windingcontinues to be energized for an interval, due to a charging current forcondenser H flowing from grounded battery l6 through resistor 68,operating winding of polarized relay B1, condenser H and resistor 12 toground. When the armature of polarized relay 6! has moved intoengagement with the front contact 13, ground is connected through thearmature and contact 13 directly to the biasing winding of polarizedrelay i9, shortcircuiting the resistor 22 through which the biasingwinding of relay i9 previously received energizing current. The currentthrough the biasing winding of relay I9 is thus increased to such avalue that the operating winding of relay l9 cannot move the armature ofthat relay into engagement with contact 23 as long as the armature ofrelay 6'! remains in engagement with contact l3.

The removal of battery from the oscillatory circuit due to movement ofthe armature of polarized relay i9 out of engagement with contact 23permits inductance 21 and the condenser or condensers included in theoscillatory circuit to set up oscillations. Since the grids 35 and 31 ofamplifier tube 38 are connected respectively to the inductive andcapacitative branches of the oscillatory circuit, biasing voltages areapplied to the grids in accordance with the oscillatory current. Theplates 4| and M controlled respectively by the grids 36 and 31 ofamplifier tube 38 are connected to the vertical and horizontal beamdeflecting plates, respectively, of cathode ray tube 43 so thatpotentials are applied to the plates 42 and 46 corresponding to theoscillatory current. The combination of resistors in the oscillatorycircuit is such as to apply to the vertical deflecting plate, a voltagewhich is in quadrature with and equal in magnitude to the potential'tinues.

applied to the horizontal deflecting plate. The constants of theoscillatory circuit are such that the circuit oscillates at an integralnurber of cycles, one or more, per impulse of the incoming permutationcode signal. As long asthe armature of polarized relay i9 remains out ofengagement with the contact 23, no energy from battery H5 is put intothe oscillatory circuit and therefore the energy within the circuitdecreases steadily and logarithmically as oscillation con- The result ofthese conditions of the oscillatory circuit is that the electron beamtraces on the screen of the cathode ray tube 63 a logarithmic spiral atthe rate of one or more complete revolutions per impulse of the incomingsignal.

Since the potentiometer resistor 3i and the secondary of feedbacktransformer 29 are connected in the oscillatory circuit, oscillatorycurrent flows in this circuit. The slider iii of potentiometer resistor3i takes oil a part of the voltage through the potentiometer 3i andapplies it to the grid of amplifier tube 86. Plate current results inthe plate circuit of amplifier tube 96 and this current is oscillatoryin accordance with the oscillating potential derived by the slider illof potentiometer 3i. Since the primary of feedback transformer 29 isincluded in the plate circuit of amplifier tube 86, the transformerfeeds oscillatory energy into its secondary winding and thus into theoscillatory circuit through the resistors 3| and 32 and through theinductance 21. The condenser 93 which shunts the primary winding offeedback transformer 9i adjusts the phase of the oscillatory current fedinto the secondary circuit of transformer 29 so that the currentdelivered to the oscillatory circuit by amplifier tube 86 is in phasewith the original oscillatory current in the oscillatory circuit. Thusthe feedback circuit acts as a negative resistance and lowers thedecrement of the oscillatory circuit. In practice the gain of thefeedback circuit is so adjusted as to compensate for the differencbetween the direct current resistance of the inductive branch of theoscillatory circuit and its resistive component at the frequency ofoscillation.

In Fig. 2 the solid line represents the oscillatory voltage appliedbetween the vertical deflecting plates 42 and Mi and the broken linerepresents the oscillatory voltage applied between the horizontaldeflecting plates 46 and 96. It will be noted that as previously stated,the voltage which controls horizontal deflection of the electron beamleads the voltage which controls vertical deflection of the beam by 90degrees. It will also be noted that the magnitude of the oscillatoryvoltages diminishes logarithmically throughout the interval allotted toa complete start-stop permutation code signal combinatlon.

In Fig. 4 the broken line indicates the path of the electron beamproduced by the voltages derived from the sweep circuit, which includesthe oscillatory circuit, the deflection voltage amplifier and thefeedback amplifier. As previously stated the electron beam path, whichis indicated by-the broken line, is in the form of a logarithmic spiral,each convolution of which is completed in the interval allotted to oneimpulse of a permutation code combination. It will be noted that thereare six full convolutions and a fraction of a seventh, which representthe start impulse, the five code impulses and the stop impulse. Thestarting point of the beam is located outside the screen of the tube. inorder that the transition from marking condition of the stop impulse toarmature in that position, decreases to the value oi the current throughthe biasing winding of the relay by the time the middle of the stopimpulse of the received permutation code signal has been reached.Further decrease of the charging current for condenser Iii decreases thecontrol of the operating winding of the relay over its armature andpermits the biasing winding to assume control, whereupon the armature isreturned to engagement with contact 88. At this time the armature ofpolarized relay M, which has been following the permutation code signalto control the intensity of the electron beam in a manner which will bedescribed later, has returned to engagement with contact H as a resultof the energlzatlon of the operating winding of relay .II by the'stopimpulse. The restoration of the armature of polarized relay $1. toengagement with contact 8% results in the reduction of current in thebiasing winding of polarized relay I9 due to removal of the shunt aroundresistor 22 and the energized operating winding of relay I9 restores itsarmature to engagement with contact 2%. Thus battery is applied to theoscillatory circuit, battery current again flows through resistors it,32, t3 and at, the inductance 21 and the transformer winding, and thecondenser 28 and any others of the condensers It, I5 and i6 that areconnected in parallel with condenser 28 are restored to fully chargedcondition. Oscillation in the oscillatory circuit is thus terminated andthe resistor 26 is of such value that the currents and voltages of theoscillatory circuit are caused to return to their steady state in acritically damped manner so that the system will be restored rapidly tothe initial condition, applying to the horizontal and vertical electronbeam defleeting plates t8 and t2, the potentials which they had at thebeginning of the signal, whereby the electron beam is restored to itsinitial position at the top and outside limits of the screen of thecathode ray tube, which is represented by the solid line circuit in Fig.4:. The damping is such that the beam will be restored to initialposition in one impulse interval, whereas the discharging time duringwhich the beam is rotated is as long as a full code combinationinterval.

It will be apparent from the foregoing description that the pathtraversed by the electron beam of the cathode ray tube t3 is the samefor all signal combinations received and is entirely independent of thecombinations of marking and spacing impulses which make up the signal.The tracing of the path by the electron beam is initiated by the startimpulse of a received permutation code signal combination and thereafterthe path is derived solely from the operation of the oscillatorycircuit. The composition of the signals is utilized for controlling theintensity of the electron beam and it is the control of the intensity ofthe beam that causes it to become visible upon the screen of the cathoderay tube 63. Normally the control grid I06 is biased negatively to asufflcient extent that the beam would not be cludes the resistor 2|.

visible upon the screen even if tracing a path within the area of thescreen, it being remembered that when the polarized relay II isresponsive to a steady marking condition not representing a group ofimpulses of a start-stop code signal combination, the beam is deflectedoutside the limits of the screenl The point of impingement of theelectron beam upon the screen is rendered visible by making the controlgrid I05 more positive and is restored to invisibility by reducing thepotential on the control grid.

Potentials for rendering the control grid I06 more positive andtherefore rendering the point of impingement of the electron beam uponthe screen of cathode ray tube t3 visible are applied through thecontacts H t or I I8 of the keys II! and H8, respectively, and throughhalf wave rectifier H8, retardation coil H2 and condensers III' and IN.The positive impulses for rendering the point of impingement of theelectron beam visible are produced in response to transitions frommarking to spacing or spacing to marking con dition of the polarizedreceiving relay II, and the key H8 is arranged to permit observation ofspring I26 out of engagement with spring I21,

and that key II'I remains unoperated. With the armature of polarizedrelay II in engagement with contact il in response to a marking signal,current will flow through the previously described energizing circuit ofpolarized relay I9 which in- The resistance value of the operatingwinding of relay I9 is a small fraction of the resistance value ofresistor 2| so that the potential diiference across the operatingwinding of relay It causes the spring I28 of key H8 to be at a potentialslightly above ground potential. This potential is supplied through halfwaverectifier H3 and inductance II2 to condenser III, and is notsumcient to raise the potential of control grid I06 of the cathode raytube to a value that will render the electron beam visible. Whenpolarized relay II responds to a spacing signal and the armature of therelay is moved out of engagement with contact II, the circuit of theoperating winding of relay I9 is interrupted and therefore currentceases to flow through resistor 2i. When the armature of relay i Iengages contact I8, current flows from battery I8 through batteryconductor It, resistor l23, springs l2l and H9 of key I", resistor I22,contact I8 of relay II and armature of that relay to ground. Theresistance value of resistor I23 is the same as that of resistor 2I andthe resistance value of resistor I22 is the same as that of theoperating winding of relay I9, so that a steady drain on battery I8 ismaintained regardless of which or the contacts I I and I8 the armatureof relay II engages. The flow of current through the substituteresistors I22 and I23 has no present efiect other than to maintain asteady potential difference "across battery I6 regardless of whether thereceiving relay II is responding to a marking or spacing condition. Theinterruption of the circuit of the operating winding of relay I9 andresulting cessation of current through resistor 2I reduces to or nearzero the potential difference across this resistor. Accord in y, thefull potential of the battery is applied through springs I28 and H6 ofkey H8 and through half wave rectifier H2 and retardation coil II2 tocondenser III. Condenser ill thus becomes charged, the charging currentreturning to ground through resistor I00, and the positive potential isapplied to the control grid I66 of the cathode ray tube 63 throughcondenser I01 to increase the intensity of the electron beam to a valuewhich will render its point of impingement, upon the-screen of the tubevisible. The relative values of the retardation coil I I2, condenser III and resistor I06 are so chosen that the circuit is verynearlycritically dammd. The potential therefore rises very rapidly, becomesnearly constant for a short interval and falls to zero with rapidityalmost equal to the rise, thus producing a sharply defined spot on thescreen. This pulse is in the direction in which the half wave rectifierH6 is connected to accommodate a flow of current and hence the rectifierpresents low impedance to the charging current for the condenser III.

When the receiving relay II again responds to a marking impulse andmoves its armature into engagement with contact I'I, current flowsthrough the operating winding of relay I6 and through resistor 2|, andthe potential applied to the upper terminal of the half wave rectifier II3, drops to the former value only slightly above ground. The potentialacross condenser III at this instant is considerably in excess of thepotential applied to the upper terminal of the half wave rectifier andaccordingly the condenser seeks to discharge. The discharging current isin the reverse direction and therefore a negative potential is againapplied to the control grid I06 02 the cathode ray tube 03 to render thepoint of impingement of the electron beam upon the screen of the tubeinvisible. The half wave rectifier H3 offers high impedance to the fiowoi the discharge current in the opposite direction and therefore thefiow of discharging current is prolonged over an extended interval ascompared with the interval during which condenser III became charged.The prolongation of the discharging interval prevents chattering of thecontacts of polarized relay I I, which might occur incident to movementof the armature into engagement with the contact I1, from rechargingcondenser Ill during the discharging interval and thus prevents theproduction of unwanted visible spots upon the screen of the cathode raytube. From the foregoing it will be apparent that with key IIO operated,a visible spot will appear on the screen of the cathode ray tube 66 inresponse to each transition from marking to spacing condition as theelectron beam traces its invisible spiral path and that no visible spotwill be produced in response to transitions from spacing to markingcondition.

When it is desired to observe transitions from spacing to markingcondition, key H6 is restored to unoperated condition and key H1 isoperated, thus bringing its movable spring I I9 into engagement with itsstationary spring [I6 to connect the right-hand end of resistor I22, theleft-hand end of which is connected to contact I8 to the upper terminalof the half wave rectifier H6.

Upon the restoration of key -I B to normal, the upper end of resistorI23 is connected to the right-hand end of resistor I22 through springsI26 and I21. With this circuit arrangement, when the armature of relayII moves from contact II to contact I8, and interrupts the energizingcircuit of the operating winding of relay I6,

asoasv I22 whereby current flows through those re sisters and since theresistance value of resistor I22 is a small fraction of that of resistorI26, the potential applied to the upper terminal of the half waverectifier H3 through springs H9 and H6 of key II! is only slightly aboveground and the charging current for condenser I II is insufllcient toraise the potential of control grid I66 of the cathode ray tube to avalue which will render the electron beam visible upon the screen.However, when a spacing signal causes the armature of relay II to moveout of engagement with contact I6 and into engagement with contact I'I,current will cease to flow through resistors I26 and I22 and thepotential applied to the upper terminal of the half wave rectifier willbe that of the positive end of battery I6 since there is no potentialdiflerence across resistor I26. Char ing current for condenser III willtherefore flow and the potential of control grid I06 will be raised tocause the point of impingement of the electron beam upon the screen ofthe tube to become visible. When, in response to the next spacingsignal, the armature of relay II again engages contact I6, the potentialof the upper terminal of the half wave rectifier will be reduced to avalue near ground potential and condenser III will discharge slowly toreduce the potential of control grid I06 and render the beam invisibleupon the screen of tube 30 regardless of subsequent chattering oi thearmature of relay II on contact I6.

It is possible to observe transitions from marking to spacing conditionand from spacing to marking condition by placing both of the keys Illand H6 in the operated condition. With this circuit arrangement theoperating winding of polarized relay I0 and its companion resistor I22are both connected to the upper terminal of the half wave rectifier N3,the former through the springs H6 and I26 of key H6 and the latterthrough springs H6 and H9 of key Ill. Under these circumstances uponmovement of the armature of relay II out of engagement with contact Ill,the full potential of battery I6 is applied to the half wave rectifierthrough resistance 2|. Charging current flows through condenser III andthe potential of control grid I06 is momentarily raised to cause avisible spot on the screen of the tube. As soon as the armature of relayI l engages contact I6, a circuit is completed from grounded battery I6through battery conductor I0, resistor 2|, springs I26 and H6 of key H6,springs H6 and N9 of key II'I, resistor I22, armature of relay II toground. From this it will be apparent that the charging of condenser IIItake place only during the transition of the armature of relay II fromcontact I! to contact I0 and that as soon as the armature engagescontact I6, the upper terminal of the half wave rectifier is broughtsubstantially to ground potential over the conductive path from groundedarmature of relay II through resistor I22 and springs H0 and H6 of keyIn.

The armature of relay II, now being in engagement with contact I6, willbe moved to engage contact H in response to the next marking impulse. Asthe armature leaves contact I6. current ceases to fiow through resistorI22 and the full potential 01. battery I6 is again applied to the upperterminal of the half wave rectifier H0 through resistor 2I and throughsprings I28 and II6 ofkey H6. Condenser III again becomes charged andthe control grid I06 of the cathode it completes the circuit throughresistors I26 and i6 ray tube is momentarily rendered positive to causea islble spot to appear on the screen of the tube. When armature ofrelay it engages contact ill, the energizing circuit for the operatingwinding of relay it is completed and the potential on the upper terminalof the half wave rectifier Ht applied through springs I28 and tilt ofkey lit is reduced due to the fiow of current through resistor ti andthe operating winding of relay it.- As in the case of the transitionfrom marking to spacing, the charging of condenser Mi occurs onlyduringthe transit time of the armature, and during the reception of theimpulse which caused the transit of the armature the condenser iiidischarges.

Due to the decrement of the oscillatory circuit, the electronbeam entersthe screen of the tube approximately half way through the start pulse.Thereafter each positive impulse on the intensity control electrodecauses a spot of light to become visible on the screen of the cathoderay tube, the spot being simultaneous with a transition of the relay ii.If the signals are without bias or distortion, the visible spotsrepresenting transitions of the relay ill will appear at the samerelative point in each convolution of the sweep circuit spiral and thevisible points will be aligned radially of the spiral at the point ofzero bias or distortion, The alignment will be radial because the sweepcircuit is so adjusted that the electron beam describes exactly oneconvolution of the spiral for each impulse of the code combination;

The dots 5%, MY, EM, MW and l5l in Fig. 4 reprev sent the transitions ofan unbiased and undistorted signal having the characteristics of thesignal shown in Fig. 3 and observed for transitions. from marking tospacing and spacing to marking. It will be observed that there is novisible point between the points Hit and ltd to represent a transitionto the fourth impulse of the code combination, since there is notransition in the code combination shown in Fig. 3, the third and fourthimpulses being of marking nature.

Bias or distortion suffered by telegraph signals usually results fromadverse lineconditions and is evidenced by lengthening or shortening ofcertain or all of the impulses of a code combination. lengthening ofmarking impulses is accompanied by shortening of spacing impulses andconversely lengthening of spacing impulses is accompanied by shorteningof marking impulses of a code combination. Any such distortion oftelegraph signals will cause the visible point representing a transitionfrom one type of impulse to the other to deviate from a radial line onthe screen of the cathode ray tube. If all marking impulses of a signalcombination are equally distorted as in biased signals, the transitionsfrom marking to spacing will be aligned along one radius and thetransitions from spacing to marking will be aligned along anotherradius. If only one impulse of a code combination is distorted, avisible point representing its transition will be out of radialalignment with points representing the transitions of the remainder ofthe signal.

The 360 degrees of angle from the zero position represents the extent towhich an impulse may be During the reception of telegraph signalingimpulses aflected by fortuitous distortion, the spots appear to jump orwander over substantial areas of the screen of the cathode ray tube. Asan aid in observing maximum deviation or displacement of a spot from thereference position, a semicircular mask may be put over the screen insuch manner that it obscures substantially all of the spots. The maskmay then be adjusted so that only the spot having the farthest deviationfrom the reference point is visible at its edge. This enables thedeviation of this particular spot to be readily observed on the scale.

In Fig. 3 the reference line I66 indicates the interval relative to thestart-stop permutation code signal represented in Fig. 3 during whichthe armature of polarized relay I9 is held in engagement with the frontcontact 26, due to the application to the biasing winding of that relayof direct ground connection through the armature and contact 73 ofpolarized relay 61, rather than through the resistor 22, Reference lineI61 indicates the interval during which the armature of relay I9 engagesthe back contact 23 and in this interval the relay I9 is responsive tocontrol by the receiving relay ii.

In Fig, 4 the portion I68 of the broken line representing the trace ofthe electron beam of the cathode ray tube 3 3 indicates the path of thebeam returning to normal or initial position following the reengagementof the armature of relay IS with its left-hand contact 23, which occursduring but not in response to reception of the stop impulse at the endof the signal combination. In Fig. 2 the sharply rising solid line atthe right of that figure and descending broken line represent thevoltages applied to the vertical and horizontal deflecting plates,respectively of the cathode ray tube which cause the beam to trace theportion I68 at the end of its spiral path.

Instead of providing for travel of the beam in a path as indicated inFig. 4, with the beginning of the path outside the limits of the screenand the terminus of the path near the center of the screen of the tube,the beginning of the path may be brought inside the screen by reducingthe gain of the triodes comprising the tube 38 and the pitch of thespiral may be reduced to zero by so adjusting the potentiometer arm 8|as to increase the feedback obtained from the tube 86 throughtransformer 29. Then the path of the beam will be circular and thevisible points produced by undistorted signals will appear at a singlepoint rather than along a radius of the screen.

If the frequency of the oscillatory circuit is so adjusted that theelectron beam makes two revolutions during each received impulse, the360 degrees of thescreen will represent 50 per cent of a, pulse length.In this manner, by causing the beam to rotate two or more times duringeach received impulse, the scale representing small values of distortionmay be greatly magnified.

Although a specific embodiment of the invention has been disclosed inthe drawings and described in the foregoing specification, it is to beunderstood that the invention is not limited to such specific embodimentbut is capable of modification, rearrangement and substitution of partsand elements without departing from the spirit of the invention andwithin the scope of the appended claims;

What is claimed is:

1. A start-stop telegraph signal distortion indicator having incombination a source of startstop ermutation code signals composed ofimpulse transitions, means for receiving said signals, a cathode raytube, oscillator means activated once per received permutation codecombination of signals for causing the ray oi said tube to travel in anarcuate path, means for normally maintaining the intensity of said rayat a level to render it invisible on the screen of said tube, and meansfor transiently increasing the intensity of said ray in response to thereception of an impulse transition to render said ray visible on thescreen of the tube.

2. A start-stop telegraph signal distortion indicator having incombination a source of startstop permutation code signals composed ofimpulse trarisitions, means for receiving said signals, a cathode raytube, means activated once per received code combination of signals forcausing the ray of said tube to travel unidirectionally in an arcuatepath, means operable independently of received signals for terminatingthe travel of said ray at the end of a received signal combination,means for normally maintaining the intensity of said ray at a level torender it invisible on the screen of the tube, and means for transientlyincreasing the intensity of said ray in response to the reception of animpulse transition to render said ray visible on the screen of the tube.

3..In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tube,an wcillator circuit for applying to said cathode ray tube electron beamdeflecting voltages of equal magnitude and in quadrature, means forconnecting across said oscillator circuit a source of steady potentialto produce a predetermined initial deflection of said electron beam,means controlled by said signal receiving means for disconnecting saidsource of potential from said oscillator circuit to permit said circuitto oscillate and apply decreasing oscillatory voltages to said cathoderay tube whereby to deflect said electron beam in a spiral path, andmeans controlled by said signal receiving means for increasing theintensity of said electron beam in response to signaling currenttransitions.

4. In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tube, adamped oscillatory circuit for applying to said tube diminishingvoltages in quadrature and equal in magnitude for causing the electronbeam in said tube to be deflected in a spiral path, means controlled bysaid signal receiving means for initiating oscillation of saidoscillatory circuit, and means also controlled by the signal receivingmeans for increasing the intensity of said electron beam in response tosignaling current transitions.

5. In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tube, adamped oscillatory circuit connected to said tube for applying theretodiminishing oscillatory voltages in quadrature and equal in magnitudefor causing the electron beam in said tube to be said tube, and meanscontrolled by said signal aacaaar receiving means for increasing theintensity of said beam in response to signaling current transitions torender said beam visible on said screen.

6. In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tube, adamped oscillatory circuit connected to said tube for applying theretodiminishing oscillatory voltages in quadrature and equal in magnitude atthe rate of an integral number of cycles per normal telegraph signalimpulse interval for causing the electron beam in said tube to bedeflected in a spiral path, means controlled by said signalreceivingmeans for initiating oscillation of said circuit, meansoperable independently of said signal receiving means for limitingoscillation of said circuit to an interval equalto that allotted to atelegraph signal code combination, means for normally maintaining theintensity of the electron beam of said tube at a level to render itinvisible on the screen of said tube, and means controlled by saidsignal receiving means for transiently increasing the intensity of saidbeam in response to signaling current transitions to render said beamvisible on said screen.

7. In a telegraph signal distortion indicator. means for receiving equallength permutation code telegraph signals composed of currenttransitions, a cathode ray tube, a damped oscillatory circuit connectedto said tube for applying thereto diminishing oscillatory voltages inquadrature and equal in magnitude at the rate of one cycle per normalimpulse of said code for causing the electron beam in said tube to bedeflected in a spiral path, means controlled by said signal receivingmeans for initiating oscillation of said circuit, means operable duringreception of a code combination but independently of said signalreceiving means for limiting oscillation of said circuit to an intervalequal to that allotted to a permutation code signal, means for normallymaintaining the intensity of the electron beam at a level to render itspoint of impingement on the screen of the tube invisible, and meanscontrolled by said signal receiving means for transiently increasing theintensity of said beam in response to signaling current transitions torender points of impingement of said beam with said screen visible atcorresponding points in the convolutions of said spiral path forundistorted signaling impulses.

8. In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tubeincluding electrical potential responsive means for controlling theintensity of the electron beam of said tube, means for normally ap lyinga predetermined potential to said intensity controlling means, meanscontrolled by said signal responsive means for increasing the potentialapplied to said intensity controlling means, and means connected betweensaid potential increasing means and said intensity controlling means fornullifying the effect upon said intensity controlling means ofchattering of said signal responsive means.

9. In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tubeincluding electrical potential responsive means for controlling theintensity of the electron beam of said tube, means for normally applyinga predetermined potential to said intensity controlling means, meanscontrolled by said signal responsive means for increasing the potentialapplied to said intensity controlling means, and means offering ass-was?low resistance to the flow of electrical current in one direction andhigh resistance to the flow of electrical current in the oppositedirection contube, means for normally applying a predetermined potentialto said intensity controlling means, means including electrical energystoring means controlled by said signal responsive means for increasingthe potential applied to said intensity controlling means in response tosignaling current transitions, and means associated with said electricalenergy storing means for retarding the discharging of energy by saidstoring means to nullify the efiect upon said intensity controllingmeans of chattering of said signal responsive means.

11. In a telegraph signal distortion indicator, means for receivingtelegraph signals composed of current transitions, a cathode ray tubeincluding electrical potential responsive means for controlling theintensity of the electron beam of said 3- tube, means for normallyapplying a predetermined potential to' said intensity controlling means,means including electrical energy storing means controlled by saidsignal responsive means for increasing the potential applied to saidintensity controlling means, and half wave rectifier means connected inseries with said electrical energy storing means for readilyaccommodating the flow of current to charge said energy storing meansand for retarding the flow of current to discharge said energy storingmeans to nullify the effect upon said intensity controlling means ofchattering of said signal responsive means.

12. In a telegraph signal distortion indicator, means for receivingsignals composed of current transitions, including an element movablebetween two positions in response to current transitions, a cathode raytube including electrical potential responsive means for controlling theintensity of the electron beam of said tube, means for normally applyinga predetermined potential to said intensity controlling means, means forapplying an increased potential to said intensity controlling means,means for causing. said increased potential to be applied to saidintensity .2

controlling means upon movement of said element from one position to theother, and means for causing said increased potential to be applied tosaid intensity controlling means upon movement of said element from saidother position to said one position.

13. In a telegraph signal distortion indicator, means including anelement movable between two positions for receiving telegraph signalscomposed of current transitions, a cathode ray tube having means forcontrolling the intensity of the electron beam of said tube, a circuitfor controlling said intensity controlling means, means controlled bysaid element for energizing said circuit,

selectively operable means for causing said circult to be energized fromsaid energizing means upon transition of said element in one directionand to be cleenergized upon the next transition oi! said element, andselectively operable means for causing said circuit to be energized fromsaid energizing means upon transition of said element in the otherdirection and to be deenergized upon the next transition of saidelement.

14. In a telegraph signal distortion indicator, means for receivingpermutation code telegraph signals composed of impulse transitions, acathode ray tube, means for imparting to the ray of said tube apredetermined initial deflection, means activated once per received codecombination of signals for causing the ray of said tube to travelunidirectionally in an arcuate path, means operable independently ofreceived signals for terminating the travel of said ray at the end of areceived signal combination, and means for critically damping saidtravel causing means to energization, whereby to cause said ray to berestored to said initial position in an interval equal to a smallfraction of the interval of reception of a code combination.

15. In a telegraph signal distortion indicator, means for receivingpermutation code telegraph signals composed of impulse transitions, acathode ray tube, means for causing the ray of said tube to be deflectedto a predetermined initial position, oscillator means activated once perreceived code combination of signals for causing the ray of said tube totravel unidirectionally in an arcuate path, means operable independentlyof received signals for terminating the travel of said ray at the end ofreceived signal combination, and means for critically damping saidoscillator means to energization, whereby to cause said ray to berestored to said initial position in an interval less than an impulseinterval of a permutation code combination.

16. In a telegraph signal distortion indicator, means for receivingpermutation code telegraph signals composed of impulse transitions, acathode ray tube, means for causing the ray of said tube to be deflectedto a predetermined initial position, oscillator means activated on perreceived code combination of signals for causing the ray of said tube totravel unidirectionally in an arcuate path, means operable independentlyof received signals for terminating the travel of said ray at the end ofa received signal-combination, and a resistor included in the energizingcircult of said oscillator means proportioned to damp said oscillatormeans critically to energization, whereby to cause said ray to berestored to said initial position in an interval less than an impulseinterval of a permutation code signal combination.

17. In a telegraph signal distortion indicator, means for receivingpermutation code telegraph signals composed of impulse transitions, acathode ray tube, oscillator means activated once per received codecombination of signals for causing the ray of said tube to travelunidirectionally in an arcuate path, means for damping said oscillatormeans critically to energizing current whereby to bring said ray to, aninitial position in an interval less than an impulse interval of apermutation code combination, means for prolonging the discharging ofsaid oscillatory means foran interval longer than the interval occupiedby a permutation code signal combination, and means for terminating thetravel of said ray at the end of a received signal combination.

18. In a device for receiving equal length permutation code signals, asignal responsive relay, a second relay responsive to operation of saidsignal responsive relay, normally inactive oscillator means set inoperation by said second relay and adjusted to oscillate at an integralnumber of cycles per impulse interval oi said mgnals, means controlledJointly by said signal responsive relay and said oscillator means fordisplaying signaling impulse transitions, a third relay operable underthe control oi said second relay for rendering said second relayunresponsive to said signal responsive relay, and means for limiting theoperation of said third relay substantially to a permutation code signalinterval.

19. In a device for receiving equal length permutation code signals, asignal responsive relay, a second relay responsive-to operation of saidsignal responsive relay, normally inactive oscillator means set inoperation by said second relay and adjusted to oscillate at an integralnumber of cycles per impulse interval of said signals. means controlledjointly by said signal responsive relay and said oscillator means fordisplaying signaling impulse transitions, a third relay operable underthe control of said second relay for rendering said second relayunresponsive to said signal responsive relay, and means including acondenser to be charged by energizing current for said third relay forlimiting the operation of said third relay substantially to apermutation code signal interval.

20. In a telegraph signal receiving device, a signal responsive relay.9, second relay operable by said signal responsive relay, a third relayoperable bysaid second relay for maintaining said second relay operatedindependently of control by said signal responsive relay, a normallyinactive oscillator rendered active by said second relay, meansassociated with said third relay for predeterminedly limiting theinterval during which said third relay remains operated, and a cathoderay tube controlled Jointly by said oscillator and said signalresponsive relay for registering signal responsive operation or saidsignal responsive 7 ssorssr ii. m a wav a t receiving device. a signalresiwnmve relay, a second relay operable by said signal rmponsive relay,a third relay operable by said second relay for maintaining said secondrelay operated independently of control by said signal responsive relay.said third relay having alternative energizing paths one oi whichnormally short-circuits the other, means operated by said third relayfor interrupting said one path whereby said other path becomes edective,means contained in said other path for predeterminedly limiting theinterval during which said other path remains eflective to maintain saidthird relay operated, and a cathode ray tube controlled Jointly by saidsecond relay and said signal responsive relay for registering signalresponsive operation of said signal responsive relay.

22. In a telegraph signal receiving device, a signal responsive relay, asecond relay operable by said signal responsive relay. a third relayoperable by said second relay for maintaining said second relay operatedindependently of control by said signal responsive relay, said thirdrelay having alternative energizing paths one of which normallyshort-circuits the other, means operated by said third relay forinterrupting said one path whereby said other path becomes effective tomaintain said third relay operated, a condenser contained in said otherpath for prolonging the operation of said third relay for apredetermined interval following the interruption oi said one path, anda cathode ray tube controlled Jointly by said second relay and saidsignal responsive relay for registering signal responsive operation ofsaid signal responsive relay.

